For example WO 93/05 118 discloses the intumescent properties of compositions which contain phosphoric acid esters of polyhydric alcohols. Such phosphoric acid esters are used in many different ways in industry, in particular in the sector concerning flame-proofing of plastic materials. Those phosphoric acid esters are halogen-free and are therefore particularly well suited for use as flame-proofing agents.
It is also already known, such as for example from Houben Weyl 12/2, pages 156 ff and 226 ff, for phosphoric acid esters of that kind to be produced by alcoholysis from phosphorus pentoxide and/or polyphosphoric acid and the desired polyhydric alcohols or mixtures thereof. The direct reaction of alcohols with phosphorus pentoxide however gives rise to major problems as phosphorus pentoxide is extremely reactive and therefore easily gives rise to dehydration phenomena and thus decomposition of the organic components with decoloration as far as carbon formation. In order to prevent this WO 93/05 118, instead of phosphorus pentoxide, uses mixtures of polyphosphoric acid with phosphorus pentoxide, in which respect however only a maximum of 50% of the amount of phosphorus can be introduced in the form of phosphorus pentoxide. Another possible way of reducing the reactivity of phosphorus pentoxide is described in DE-A-3 502 705 by means of a given temperature-control procedure. Japanese patent publications Nos. 04 210 221, 56 092 294 and 49 055 669 follow yet a different path insofar as they dilute the reaction mixture with tetrahydrofuran, hydrocarbons such as n-hexane, or chloroform. U.S. Pat. No. 4,153,649, DE-A-2 941 419 and DE 3 520 053 operate with excessive alcohols.
All those processes suffer from the disadvantage that subsequent to the esterification they require special purification and cleaning operations.
Therefore the basic object of the invention is to obtain phosphoric acid esters or mixtures of polyhydric alcohols without decomposition reactions and without the need for subsequent purification operations and to be able to use them in the form as they are removed from the reaction container, for the production of flame-proofing finishes.
The process according to the invention for the production of phosphoric acid esters or phosphoric acid ester mixtures of polyhydric alcohols by reaction of the polyhydric alcohols with phosphorus pentoxide is characterised in that the amount of phosphorus pentoxide which is required for the esterification operation is suspended in an amount of the ester or ester mixture to be produced, thereupon the amount of polyhydric alcohol required for the esterification operation and possibly water is added at a temperature in the range of between 20 and 180xc2x0 C., thereupon the esterification reaction is substantially completely executed and then the product is obtained.
That process can entail operating with stoichiometric or substantially stoichiometric amounts of phosphorus pentoxide, polyhydric alcohol and possibly water, so that practically only the desired ester or esters is or are produced and no subsequent separation of excess starting substances or solvents has to be effected.
The addition of polyhydric alcohol and optionally water is advantageously effected at a temperature in the range of between 20 and 150xc2x0 C., and subsequent completion of the esterification reaction is desirably implemented for a period of between 1 and 6 hours at at least the temperature of the addition of polyhydric alcohol. Desirably, in completing the esterification reaction, heating and agitation are effected until a clear fluid has occurred, which shows that the reaction was completely implemented.
When the reaction is concluded the freshly produced amount of phosphoric acid ester or phosphoric acid ester mixture is removed from the reaction container. Thereupon the residual amount of phosphoric acid ester or mixture which has remained in the reaction container can be used to begin a fresh start for the reaction by phosphorus pentoxide being freshly added and suspended in the finished ester or ester mixture.
In particular for further use for the production of flame-proofing finishes, it is desirable to add small amounts of boric acid to the reaction mixture. The additional amount of boric acid is preferably between 0.2 and 6% by weight, preferably being about 3% by weight with respect to the total amount of added phosphorus pentoxide, polyhydric alcohol and optionally water. In a fire situation, in particular in relation to flame-proofing finishes for cellulose materials, the boron component in the esters or ester mixtures produced in accordance with the invention prevents the fire from continuing to glow afterwards and suppresses the formation of fumes.
The polyhydric alcohols used for the process according to the invention are for example and desirably ethane-1,2-diol, propane-1,2- and 1,3-diol, butane-1,2-, -1,3-, -1,4- and -2,3-diol, glycerine, trimethylolmethane, -ethane and -propane, neopentylglycol, erythritols, pentaerythritol, di- and polypentaerythritols, pentitols such as arabitol and xylitol, hexitols such as mannitol and sorbitol innositols, dihydroxybenzols and 2,3-dimethylol-1,3-dihydroxybenzol as well as mixtures thereof.
In many cases the combinations of the phosphoric acid esters or ester mixtures produced in accordance with the invention, with polyvinyl amine or polyethylene imine, are found to be advantageous in particular for further use for the production of flame-proofing finishes. Melamine and guanidine salts of the phosphoric acid esters are found to be suitable, in combination with the phosphoric acid esters produced in accordance with the invention. Those additives are thermally stable and can therefore be incorporated into melted-on plastic materials. Methylol melamines and the precondensates thereof can also be combined with the phosphoric acid esters produced in accordance with the invention and used to produce flame-inhibiting treatments.
For example phenol, melamine or urea formaldehyde resins, polyacrylate or polyvinyl acetate dispersions or epoxy resins are suitable as binding agents for the flame-proofing treatment.
Preferably the phosphoric acid esters or mixtures produced in accordance with the invention are used for the production of a flame-proofing treatment of or finish on laminate composite materials.
Laminate composite materials are used in many sectors as in the packaging sector, in the domestic, sporting, technological and building areas but also in aircraft, automobile and apparatus engineering, in cooling technology and in relation to highly stressed machine parts. The large number of possible forms and number of conceivable combinations of starting materials afford a wide spectrum in terms of areas of use. Primarily wood, metals, glass as well as inorganic and organic polymers fall to be considered as constituents of such laminate composite materials. The laminate composite systems also include laminates of the most widely varying kinds, moulded laminate material, corrugated cardboard or fibreboard, packaging crepe, thermal wallpapers, roof insulations, non-woven fabric combinations involving the most widely varying kinds of stabilisation, sandwich components, lined or coated textiles, cable sheathings and many others.
The binding agents used for fixing the phosphoric acid esters and mixtures produced in accordance with the invention can also be used at the same time as binding agents for the lamination of various materials. For the production of laminates the carrier or backing materials can be impregnated by dipping or lacquering or coating and hardened for example at temperatures of between 100 and 200xc2x0 C. in presses.
When using the phosphoric acid esters or mixtures produced in accordance with the invention for flame-proofing treatments desirably between 10 and 40% of the phosphoric acid esters or mixtures is added to the binding agent system. The additional amounts of binding agent can be reduced by pre-impregnation of the carrier material. Optimum flame-proofing is achieved if both the carrier material and also the cover layers of the composite material contain the phosphoric acid esters or mixtures thereof which are produced in accordance with the invention.
Non-woven fabrics comprising inorganic or organic fibres or mixtures thereof are desirably sprayed prior to stabilisation thereof with solutions of the phosphoric acid esters or phosphoric acid ester mixtures or with mixtures of binding agent resin and phosphoric acid ester, laid and stabilised.
The flame-proofing compositions produced from the phosphoric acid esters and mixtures which are produced in accordance with the invention afford the advantages that the flammability of the composite systems is reduced, flame formation and development is inhibited, flame propagation and spread is restricted, the predetermined structures, their integrity and function are maintained in the fire situation, a protective layer is produced which protects articles or components disposed therebeneath from the effect of flame and the development of combustible gases is prevented and in a fire situation no additional gases are produced from the composition.
In order that the invention may be more readily understood, reference is made to the following examples, which are intended to be illustrative of the invention but are not intended to be limiting in scope.